Method for producing tetrafluoromethane

ABSTRACT

A method for producing tetrafluoromethane as follows is unlikely to damage a reaction apparatus and can produce tetrafluoromethane safely, inexpensively, and stably. To a raw material liquid containing a fluorinated hydrocarbon represented by chemical formula C p H q Cl r F s  (wherein p is an integer of 3 to 18, q is an integer of 0 to 3, r is an integer of 0 to 9, and s is an integer of 5 to 30) and having no carbon-carbon unsaturated bond, fluorine gas is introduced, and concurrently a reaction inducer is introduced in a gas state, giving tetrafluoromethane. The reaction inducer is reacted with fluorine gas to induce a reaction of forming tetrafluoromethane from the fluorinated hydrocarbon and the fluorine gas and is at least one reaction inducer selected from a hydrocarbon gaseous at normal temperature and pressure and hydrogen gas.

TECHNICAL FIELD

The present invention relates to a method for producingtetrafluoromethane.

BACKGROUND ART

Known methods for producing tetrafluoromethane include a method ofreacting solid carbon with fluorine gas, a method of reacting a gaseoushydrocarbon with fluorine gas, and a method of reacting a mixture of acarbon material and a metal, a metal fluoride, or a fused alumina withfluorine gas (see PLTs 1 and 2).

The method of reacting solid carbon with fluorine gas is a combustionreaction with flames and generates a great amount of reaction heat, andthus the material itself of an outlet of fluorine gas or a reactioncontainer may be reacted with fluorine gas to corrode. A reactionwithout flames may generate insufficient reaction heat, givingtetrafluoromethane at a lower yield.

The method of reacting a gaseous hydrocarbon with fluorine gas is also acombustion reaction with flames and generates a great amount of reactionheat, and thus the material itself of an outlet of fluorine gas or areaction container may be reacted with fluorine gas to corrode. For areaction without flames, fluorine gas is diluted with an inert gas suchas nitrogen gas to suppress the reaction heat, but such a measure needsa step of separating and purifying the resulting tetrafluoroethane froman inert gas, and this increases the production cost unfortunately.

The method of reacting a mixture of a carbon material and a metal, ametal fluoride, or a fused alumina with fluorine gas is a method ofmildly reacting a carbon material with fluorine gas, is not performed insuch a reaction condition as to cut carbon-carbon bonds, and isunsuitable for the synthesis of tetrafluoromethane.

CITATION LIST Patent Literature

PTL 1: JP 6-298681 A

PTL 2: JP 11-180706 A

SUMMARY OF INVENTION Technical Problem

As described above, in conventional methods for producingtetrafluoromethane, such a vigorous reaction as to damage a reactionapparatus is performed, whereas a reaction in a mild conditionsuppresses damages on a reaction apparatus but is unlikely to givetetrafluoromethane as a main product. The present invention is intendedto provide a method that is for producing tetrafluoromethane, isunlikely to damage a reaction apparatus, and can producetetrafluoromethane safely, inexpensively, and stably.

Solution to Problem

To solve the problems, aspects of the present invention are thefollowing [1] to [3].

[1] A method for producing tetrafluoromethane, the method including

introducing fluorine gas to a raw material liquid containing afluorinated hydrocarbon represented by chemical formulaC_(p)H_(q)Cl_(r)F_(s) (in the chemical formula, p is an integer of 3 ormore and 18 or less, q is an integer of 0 or more and 3 or less, r is aninteger of 0 or more and 9 or less, and s is an integer of 5 or more and30 or less) and having no carbon-carbon unsaturated bond andconcurrently introducing a reaction inducer in a gas state,

in which the reaction inducer is reacted with the fluorine gas to inducea reaction of forming tetrafluoromethane from the fluorinatedhydrocarbon and the fluorine gas and is at least one reaction inducerselected from a hydrocarbon gaseous at normal temperature and pressureand hydrogen gas.

[2] The method for producing tetrafluoromethane according to the aspect[1], in which the reaction inducer is hydrogen gas.

[3] The method for producing tetrafluoromethane according to the aspect[1] or [2], in which the fluorinated hydrocarbon is at least onefluorine-containing substance selected from a perfluorocarbon, afluorohydrocarbon, a chlorofluorocarbon, a chlorofluorohydrocarbon, achlorotrifluoroethylene polymer, and a perfluoropolyether.

Advantageous Effects of Invention

A method according to the present invention enables safe, inexpensive,and stable production of tetrafluoromethane while being unlikely todamage a reaction apparatus.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates an embodiment of a method for producingtetrafluoromethane pertaining to the present invention and is aschematic view illustrating a structure of a reaction apparatus fortetrafluoromethane.

DESCRIPTION OF EMBODIMENTS

An embodiment of the present invention will now be described. Thepresent embodiment is merely an example of the present invention, andthe present invention is not limited to the present embodiment. Variousmodifications or improvements can be made in the present embodiment, andsuch various modifications and improvements can be encompassed by thepresent invention.

In a conventional tetrafluoromethane production method of reactingactivated carbon with fluorine gas to give tetrafluoromethane, routesthrough which reaction heat is removed from a reaction field include aroute through which heat is discharged outside via a gas heated byreaction heat in an atmosphere and a route through which heat isdischarged outside via a reaction apparatus heated by reaction heat (forexample, an outlet of fluorine gas or a reaction container). A gas,which unfortunately has a small heat capacity, discharges a small amountof heat, and most of the reaction heat is consumed in heating a reactionapparatus. As a result, a reaction apparatus has a high temperature,thus the reaction apparatus is reacted with fluorine gas, and thereaction apparatus is corroded and damaged.

The inventors of the present invention have carried out intensivestudies and consequently have found that by performing a reaction offorming tetrafluoromethane from a fluorinated hydrocarbon and fluorinegas in a liquid phase to reduce the temperature of a reaction field andby further using, in the reaction field, a reaction inducer that inducesthe reaction of forming tetrafluoromethane from a fluorinatedhydrocarbon and fluorine gas, a cleavage reaction of carbon-carbon bondsof a fluorinated hydrocarbon, which is caused only at an extremely hightemperature, can be caused in a liquid phase at a low temperature.

In other words, the inventors of the present invention have found that afluorinated hydrocarbon is difficult to react with fluorine gas evenwhen fluorine gas is blown into a liquid fluorinated hydrocarbon, butwhen a reaction inducer is used together, the reaction inducer isreacted with fluorine gas, and this reaction induces the reactionbetween a fluorinated hydrocarbon and fluorine gas at a low temperatureto give tetrafluoromethane.

The mechanism is thought as follows: When fluorine gas and a gaseousreaction inducer are blown through outlets into a liquid fluorinatedhydrocarbon, bubbles containing the fluorine gas and the reactioninducer are formed on the periphery of the outlet of fluorine gas, andin the bubbles, the fluorine gas is reacted with the reaction inducer.By the reaction heat of the reaction, the temperature of the bubblesincreases. The reaction inducer is used only at the initial stage of thereaction to increase the temperature of bubbles.

On a gas-liquid interface between the bubbles having a highertemperature and the peripheral liquid phase, the fluorine gas in thebubbles is reacted with the fluorinated hydrocarbon in the liquid phasebefore the bubbles leave the outlet of fluorine gas. By the reactionheat of the reaction, the fluorinated hydrocarbon around the bubblesvaporizes to react with the fluorine gas in the bubbles. Accordingly, aregion having a temperature higher than the temperature of the liquidphase by about 20° C. or more is formed around the outlet of fluorinegas (hereinafter called “high temperature reaction region”). When thesupply of fluorine gas is continued, the reaction between a fluorinatedhydrocarbon and fluorine gas continues in the high temperature reactionregion. The resulting reaction heat continuously volatilizes theperipheral liquid phase (i.e., the fluorinated hydrocarbon), and thusthe temperature increase of the liquid phase is supposed to besuppressed.

A method for producing tetrafluoromethane pertaining to the presentembodiment includes introducing fluorine gas to a raw material liquidcontaining a fluorinated hydrocarbon represented by chemical formulaC_(p)H_(q)Cl_(r)F_(s) and having no carbon-carbon unsaturated bond (inthe present description, also simply called “fluorinated hydrocarbon”)and concurrently introducing a reaction inducer in a gas state. Thereaction inducer is reacted with fluorine gas to induce a reaction offorming tetrafluoromethane from the fluorinated hydrocarbon and thefluorine gas and is at least one reaction inducer selected from ahydrocarbon gaseous at normal temperature and pressure and hydrogen gas.In the chemical formula, p is an integer of 3 or more and 18 or less, qis an integer of 0 or more and 3 or less, r is an integer of 0 or moreand 9 or less, and s is an integer of 5 or more and 30 or less.

Even when a fluorinated hydrocarbon is difficult to react with fluorinegas, the above mechanism allows the reaction between a reaction inducerand fluorine gas to induce the reaction between a fluorinatedhydrocarbon and fluorine gas even at a low temperature. Hence, thetemperature is unlikely to abnormally increase in a reaction field,fluorine gas is unlikely to damage a reaction apparatus, andtetrafluoromethane can be safely, inexpensively, and stably produced ata high yield.

In addition, the reaction apparatus is not required to be made from anexpensive material having corrosion resistance against fluorine gas (forexample, a nickel alloy, Hastelloy (registered trademark), or Monel(registered trademark)), and a reaction apparatus can be made from ageneral steel such as stainless steel, giving an inexpensive reactionapparatus.

The resulting tetrafluoromethane is useful, for example, as an etchingagent for substrates and a cleaning agent for chambers in thesemiconductor production process.

Hereinafter, the method for producing tetrafluoromethane pertaining tothe present embodiment will be described in further detail.

(1) Fluorinated Hydrocarbon

The fluorinated hydrocarbon is a saturated hydrocarbon represented bychemical formula C_(p)H_(q)Cl_(r)F_(s) and having no carbon-carbonunsaturated bond. The fluorinated hydrocarbon may be any of a linearhydrocarbon, a branched hydrocarbon, and a cyclic hydrocarbon and may bea compound containing no hydrogen atom or no chlorine atom. Examples ofthe fluorinated hydrocarbon include at least one fluorine-containingsubstance selected from a perfluorocarbon, a fluorohydrocarbon, achlorofluorocarbon, a chlorofluorohydrocarbon, a chlorotrifluoroethylenepolymer, and a perfluoropolyether.

Specific examples of the chlorotrifluoroethylene polymer include difreonoil (registered trademark), and specific example of theperfluoropolyether include Fomblin oil (registered trademark). Thedifreon oil is a polychlorotrifluoroethylene having flowability atnormal temperature (a pour point of 5 to 15° C.) and having a molecularweight of about 1,000 or less.

The fluorinated hydrocarbon may be any of a gas, a liquid, and a solidat normal temperature and pressure but is preferably a liquid. In thepresent invention, the normal temperature means 25° C., and the normalpressure means 101.325 kPa (1 atm).

When a fluorinated hydrocarbon is a liquid, the fluorinated hydrocarbonmay be used as a raw material liquid, or the fluorinated hydrocarbon maybe mixed with a solvent, and the resulting mixture of the fluorinatedhydrocarbon and the solvent can be used as the raw material liquid. Whena fluorinated hydrocarbon is a gas or a solid, a solvent is required tobe used in the reaction, and the fluorinated hydrocarbon is required tobe mixed with the solvent to give a raw material liquid. In this case, asolid fluorinated hydrocarbon may be dissolved in a raw material liquidor may be dispersed in a powder form. Alternatively, an aggregated,fluorinated hydrocarbon may be contained in a raw material liquid. Agaseous fluorinated hydrocarbon may be dissolved in a raw materialliquid or may be dispersed in a foam. In other words, in the method forproducing tetrafluoromethane pertaining to the present embodiment, thesynthesis reaction of tetrafluoromethane may be performed withoutsolvent or may be performed in a solvent.

The above fluorinated hydrocarbon is an organic compound that isdifficult to react with fluorine gas even when 100% by volume fluorinegas is blown at 40° C. and 101.325 kPa. The reaction formula of afluorinated hydrocarbon with fluorine gas is represented by thefollowing formula.

C_(p)H_(q)Cl_(r)F_(s)+(4p+q+r−s)/2F₂->pCF₄ +rClF+qHF

In consideration of the reaction formula, to efficiently use thesupplied fluorine gas to form tetrafluoromethane, q and r in thechemical formula C_(p)H_(q)Cl_(r)F_(s) are preferably small values.

When p in the chemical formula C_(p)H_(q)Cl_(r)F_(s) is 3 or more, afluorinated hydrocarbon is not a gas at normal temperature and pressurein many cases (a liquid or a solid in many cases), thus is not requiredto be cooled or pressurized to make a gas into a liquid, and iseconomical. When p is 18 or less, a fluorinated hydrocarbon is not asolid at normal temperature and pressure in many cases (a gas or aliquid in many cases), thus is not required to be warmed to make a solidinto a liquid, and is economical. p is an integer of 3 or more and 18 orless, preferably an integer of 3 or more and 10 or less, more preferablyan integer of 3 or more and 5 or less, and is economically as small aspossible because a smaller amount of fluorine gas is needed forproduction of 1 mol of tetrafluoromethane.

When q in the chemical formula C_(p)H_(q)Cl_(r)F_(s) is 3 or less, ahydrogen atom is reacted with fluorine gas to form hydrogen fluoride asa by-product at a smaller rate, and such a condition is economicalbecause a smaller amount of fluorine gas is needed for production of 1mol of tetrafluoromethane. q is an integer of 0 or more and 3 or less,preferably an integer of 0 or more and 2 or less, and more preferably 0or 1. To increase the reaction selectivity of tetrafluoromethane, thefluorinated hydrocarbon is more preferably a perfluorocarbon or achlorofluorocarbon where q is 0.

When r in the chemical formula C_(p)H_(q)Cl_(r)F_(s) is 0 or more and 9or less, a fluorinated hydrocarbon is not a solid at normal temperatureand pressure in many cases (a gas or a liquid in many cases), thus isnot required to be warmed to make a solid into a liquid, and iseconomical. In addition, a chlorine atom is reacted with fluorine gas toform fluorine chloride as a by-product at a smaller rate, and such acondition is economical because a smaller amount of fluorine gas isneeded for production of 1 mol of tetrafluoromethane. r is an integer of0 or more and 9 or less and preferably an integer of 0 or more and 4 orless. Moreover, the fluorinated hydrocarbon is more preferably aperfluorocarbon where q and r are 0.

(2) Reaction Inducer

The reaction inducer is a compound easily reacted with fluorine gas. Thereaction inducer is reacted with fluorine gas to induce the reaction offorming tetrafluoromethane from a fluorinated hydrocarbon and fluorinegas and is at least one reaction inducer selected from a hydrocarbongaseous at normal temperature and pressure and hydrogen gas. Thereaction inducer is introduced in a gas state into a raw materialliquid, and may be an inducer that is dissolved in a raw material liquidor an inducer that is dispersed in a foam.

Examples of the reaction inducer include a saturated hydrocarbon thathas 1 or more and 10 or less carbon atoms and is a gas at normaltemperature and pressure, such as methane, ethane, and ethylene, andhydrogen gas. When a hydrocarbon is used, fluorine gas is reacted withthe reaction inducer at a higher rate to reduce economic efficiency, andthus hydrogen gas is more preferred. The reaction inducer can be reactedwith fluorine gas to form tetrafluoromethane in some cases.

The reaction inducer may be introduced in any amount as long as thereaction of forming tetrafluoromethane from a fluorinated hydrocarbonand fluorine gas can be induced, and the amount is preferably 15% byvolume or less of the amount of fluorine gas introduced. When once thereaction inducer induces the reaction of forming tetrafluoromethane froma fluorinated hydrocarbon and fluorine gas, the reaction between thefluorinated hydrocarbon and the fluorine gas continues even after theintroduction of the reaction inducer is subsequently stopped. Hence,after the reaction inducer induces the reaction of formingtetrafluoromethane from a fluorinated hydrocarbon and fluorine gas, theintroduction of the reaction inducer to the raw material liquid may bestopped.

An outlet through which a gaseous reaction inducer is introduced to araw material liquid is preferably provided near an outlet through whichfluorine gas is introduced to the raw material liquid. The pipes throughwhich fluorine gas and a reaction inducer are introduced to a rawmaterial liquid in the reaction container may have any shape. Forexample, the pipe through which a gas is introduced to a raw materialliquid may be a double pipe, and one of the fluorine gas and thereaction inducer may be introduced through an inner pipe, whereas theother may be introduced through an outer pipe. Alternatively, a pipethrough which fluorine gas is introduced to a raw material liquid and apipe through which a reaction inducer is introduced to a raw materialliquid are provided in a reaction container, and the respective outletsof the pipes may be located closely.

(3) Reaction Apparatus An example of a reaction apparatus in which themethod for producing tetrafluoromethane pertaining to the presentembodiment is performed to give tetrafluoromethane will be describedwith reference to FIG. 1.

A reaction apparatus in FIG. 1 includes a metal reaction container 11 inwhich a reaction for forming tetrafluoromethane is performed, a rawmaterial liquid introduction pipe 21 through which a raw material liquid1 containing a fluorinated hydrocarbon represented by chemical formulaC_(p)H_(q)Cl_(r)F_(s) and having no carbon-carbon unsaturated bond isintroduced to the reaction container 11, a fluorine gas pipe 23 having,at an end, an outlet 23 a through which fluorine gas is introduced to araw material liquid 1 in the reaction container 11, a reaction inducerpipe 27 having, at an end, an outlet 27 a through which at least onereaction inducer selected from a hydrocarbon gaseous at normaltemperature and pressure and hydrogen gas is introduced in a gas stateto a raw material liquid 1 in the reaction container 11, and a gasdischarge pipe 25 through which a gas phase in the reaction container 11is discharged outside. Examples of the metal forming the reactioncontainer 11 include stainless steel.

The reaction apparatus illustrated in FIG. 1 further includes acirculator that extracts a portion of a raw material liquid 1 in thereaction container 11 during reaction outside the reaction container 11and returns the solution into the reaction container 11. In particular,the respective ends of a circular circulation pipe 28 are connected tothe reaction container 11, and a liquid circulating pump 15 installed onthe circulation pipe 28 sends a raw material liquid 1. The raw materialliquid 1 extracted from the reaction container 11 can be returnedthrough the circulation pipe 28 into the reaction container 11.

A heat exchanger 19 is installed at a point midway of the circulationpipe 28 and at a downstream side of the liquid circulating pump 15 andcan cool the extracted raw material liquid 1. The raw material liquid 1cooled by the heat exchanger 19 is returned into the reaction container11. In other words, the reaction apparatus illustrated in FIG. 1 isconfigured to perform reaction while a portion of a raw material liquid1 in the reaction container 11 is extracted and cooled and the cooledraw material liquid 1 is returned to the reaction container 11.

A produced gas containing tetrafluoromethane formed by reaction can bedischarged through the gas discharge pipe 25 outside the reactioncontainer 11. At a downstream side of the gas discharge pipe 25, a heatexchanger 17 is installed and can cool a produced gas discharged fromthe reaction container 11. Even when a fluorinated hydrocarbon as amaterial vaporizes and is contained in a produced gas, the fluorinatedhydrocarbon can be liquified by cooling the produced gas with the heatexchanger 17 and can be returned to the reaction container 11. Hence, anunreacted fluorinated hydrocarbon can be prevented from escaping fromthe reaction container 11 to the outside and from being lost.

The outlet 23 a of the fluorine gas pipe 23 may have any shape, and theoutlet 23 a can be a round through-hole formed on the fluorine gas pipe23. The through-hole can have a diameter of, for example, 0.5 mm or moreand 5 mm or less. The fluorine gas pipe 23 may have one or a pluralityof outlets 23 a. Near the outlet 23 a, a temperature measurement devicesuch as a thermocouple may be installed to measure the temperature nearthe outlet 23 a. The same is applied to the outlet 27 a of the reactioninducer pipe 27.

Near the outlet 23 a of fluorine gas, a high temperature reaction regionis formed as described above, and it is preferable that the hightemperature reaction region be not in contact with a member of thereaction apparatus, such as a chamber wall of the reaction container 11,a thermocouple, a stirring blade, and a baffle plate. A portion incontact with the high temperature reaction region has a highertemperature, and thus a member of the reaction apparatus may corrode.

The range of a high temperature reaction region can be represented byequation ln(LV)=a ln(L/D) (hereinafter also called equation (1)), whereD is the diameter (mm) of an outlet 23 a, LV is the blowing linearvelocity (m/s) of fluorine gas as converted at a temperature of 0° C.and a pressure of 0 MPaG, and L is the length (mm) (the length in afluorine gas ejecting direction) of a formed high temperature reactionregion. In the equation, ln is natural logarithm, and a is a constantand can be a value of 1.2 or more and 1.4 or less. From the equation,the length of an expected high temperature reaction region can becalculated, and this enables a design such that a high temperaturereaction region is not in contact with a member of the reactionapparatus.

The direction along the major axis of a high temperature reaction region(the axis along a fluorine gas ejecting direction) may be any direction,and fluorine gas is preferably ejected from the outlet 23 a at an angleof 90° (horizontal direction) or more and 180° or less so as to stablymaintain a high temperature reaction region to a maximum extent, wherethe vertically downward direction is 0°, and the vertically upwarddirection is 180°.

The reaction apparatus includes a temperature measurement device (notillustrated) for measuring the temperature of a raw material liquid 1and includes the circulator having the heat exchanger 19, and thus thereaction can be performed while a raw material liquid 1 is cooled tocontrol the temperature of the raw material liquid 1. Accordingly, anabnormal temperature increase of a reaction field or damage on thereaction apparatus can be suppressed. The temperature of a raw materialliquid 1 can be set at 0° C. or more and 200° C. or less, for example.The reaction pressure can be set, for example, at 0.01 MPaA (absolutepressure) or more and 1.0 MPaA (absolute pressure) or less andpreferably normal pressure or more and 0.9 MPaG or less.

The reaction apparatus may include a device for measuring the liquidlevel of a raw material liquid 1. For example, a device of measuring theliquid level from the differential pressure between a liquid phase and agas phase in the reaction container 11 or a device of measuring theliquid level by using a float can be used.

As the synthesis reaction of tetrafluoromethane proceeds, the liquidlevel of a raw material liquid 1 decreases. If the liquid level can bemeasured, a raw material liquid 1 can be supplied into the reactioncontainer 11 while the liquid level is continuously or intermittentlymonitored, and thus tetrafluoromethane can be continuously synthesized.

The concentration of fluorine gas used in the reaction is not limited toparticular values, and 100% fluorine gas may be used, or a fluorine gasdiluted with an inert gas such as nitrogen gas and argon may be used.Similarly, the concentration of the gaseous reaction inducer is notlimited to particular values, and 100% gaseous reaction inducer may beused, or a gaseous reaction inducer diluted with an inert gas such asnitrogen gas and argon may be used.

To uniformly react the blown fluorine gas with a raw material liquid 1,the reaction container 11 may include a stirrer having stirring bladesfor stirring the raw material liquid 1.

EXAMPLES

The present invention will next be described more specifically withreference to examples and comparative examples.

Example 1

Tetrafluoromethane was synthesized by using a reaction apparatussubstantially the same as the reaction apparatus in FIG. 1 except that aheat exchanger 19, a circulation pipe 28, and a liquid circulating pump15 were not included. In an SUS reaction container having a capacity of1 L, 600 mL (1,030 g) of perfluoro-n-octane having a boiling point of103° C. at normal pressure was placed as a raw material liquid.

From an outlet having a diameter of 1 mm and provided at an end of thefluorine gas pipe, fluorine gas was introduced to the raw materialliquid. Concurrently with the introduction of fluorine gas, hydrogen gaswas introduced to the raw material liquid from an outlet having adiameter of 1 mm and provided at an end of the reaction inducer pipe.The outlet of the reaction inducer pipe was located near (at a position2 mm apart from) the outlet of the fluorine gas pipe. The blowing flowrate of fluorine gas was set at 400 mL/min as converted at a temperatureof 0° C. and a pressure of 0 MPaG, and the blowing linear velocity wasset at 2.1 m/s. The blowing flow rate of hydrogen gas was set at 20mL/min as converted at a temperature of 0° C. and a pressure of 0 MPaG,and the blowing linear velocity was set at 0.1 m/s. In the reaction, theintroduction amount of hydrogen gas was 5% by volume relative to theintroduction amount of fluorine gas.

When the value a in equation (1) is 1.27, a high temperature reactionregion having a length of 1.8 mm is expected to be formed for eachoutlet. Hence, in the range where the high temperature reaction regionswere to be formed, any member of the reaction apparatus was not placedexcept a single thermocouple.

When the introduction of fluorine gas and hydrogen gas was started, thetemperature of the fluorine gas outlet increased to 200° C., and thusthe introduction of hydrogen gas was stopped. The reaction continuedwhile the reaction container was cooled from the outside, and thereaction was performed while the temperature of the raw material liquidwas maintained at 25° C., and the reaction pressure was maintained atnormal pressure. As a result, the reaction was performed while thetemperature of the fluorine gas outlet was maintained at 200° C. evenafter the introduction of hydrogen gas was stopped.

The produced gas was sampled and analyzed, and consequently the producedgas contained 95% by volume tetrafluoromethane and 5% by volumehexafluoroethane. Of the reacted perfluoro-n-octane, 95 by mole wasconverted into tetrafluoromethane, and the yield of tetrafluoromethanewas 95%. No unreacted fluorine gas was detected in the produced gas.

After the completion of the reaction, the outlet of the fluorine gaspipe was observed. No corrosion or the like was observed, and the outletmaintained the same shape as the shape before the reaction. In addition,no corrosion or the like was observed on the thermocouple for measuringthe temperature of the fluorine gas outlet or the raw material liquidand on the reaction container.

Comparative Example 1

Reaction was performed in the same manner as in Example 1 except that noreaction inducer (hydrogen gas) was introduced. Although introduction offluorine gas was continued for 5 hours, the temperature of the fluorinegas outlet was not changed, and the entire amount of the introducedfluorine gas was discharged in an unreacted state from the gas dischargepipe for discharging a gas phase in the reaction container to theoutside. In the discharged fluorine gas, no tetrafluoromethane wasdetected, and the yield of tetrafluoromethane was 0%.

Example 2

Tetrafluoromethane was synthesized by using a reaction apparatussubstantially the same as the reaction apparatus in FIG. 1 except that aheat exchanger 19, a circulation pipe 28, and a liquid circulating pump15 were not included. In an SUS reaction container having a capacity of1 L, 600 mL (1,000 g) of a chlorofluorobutane mixture having thefollowing formula was placed as a raw material liquid. In other words,the chlorofluorobutane mixture is a mixture containing 20% by masstrichloroheptafluorobutane, 5% by mass dichlorooctafluorobutane, 70% bymass pentachloropentafluorobutane, and 5% by masstetrachloropentafluorobutane. The chlorofluorobutane mixture is aby-product formed when tetrachlorohexafluorobutane is synthesized byreaction of tetrachlorobutane with fluorine gas.

From an outlet having a diameter of 1 mm and provided at an end of thefluorine gas pipe, fluorine gas was introduced to the raw materialliquid. Concurrently with the introduction of fluorine gas, hydrogen gaswas introduced to the raw material liquid from an outlet having adiameter of 1 mm and provided at an end of the reaction inducer pipe.The outlet of the reaction inducer pipe was located near (at a position2 mm apart from) the outlet of the fluorine gas pipe. The blowing flowrate of fluorine gas was set at 600 mL/min as converted at a temperatureof 0° C. and a pressure of 0 MPaG, and the blowing linear velocity wasset at 3.2 m/s. The blowing flow rate of hydrogen gas was set at 60mL/min as converted at a temperature of 0° C. and a pressure of 0 MPaG,and the blowing linear velocity was 0.32 m/s. In the reaction, theintroduction amount of hydrogen gas was 10% by volume relative to theintroduction amount of fluorine gas.

When the introduction of fluorine gas and hydrogen gas was started, thetemperature of the fluorine gas outlet increased to 300° C., and thusthe introduction of hydrogen gas was stopped. The reaction continuedwhile the reaction container was cooled from the outside, and thereaction was performed while the temperature of the raw material liquidwas maintained at 60° C., and the reaction pressure was maintained atnormal pressure. As a result, the reaction was performed while thetemperature of the fluorine gas outlet was maintained at 300° C. evenafter the introduction of hydrogen gas was stopped.

The produced gas was sampled and analyzed, and consequently the producedgas contained 80% by volume tetrafluoromethane and 20% by volumechlorotrifluoromethane. No unreacted fluorine gas was detected in theproduced gas, but chlorine fluoride and hydrogen fluoride were detected.

After the completion of the reaction, the outlet of the fluorine gaspipe was observed. No corrosion or the like was observed, and the outletmaintained the same shape as the shape before the reaction. In addition,no corrosion or the like was observed on the thermocouple for measuringthe temperature of the fluorine gas outlet or the raw material liquidand on the reaction container.

Comparative Example 2

Reaction was performed in the same manner as in Example 2 except that noreaction inducer (hydrogen gas) was introduced. Although introduction offluorine gas was continued for 5 hours, the temperature of the fluorinegas outlet was not changed, and the entire amount of the introducedfluorine gas was discharged in an unreacted state from the gas dischargepipe for discharging a gas phase in the reaction container to theoutside. In the discharged fluorine gas, no tetrafluoromethane wasdetected, and the yield of tetrafluoromethane was 0%.

REFERENCE SIGNS LIST

-   -   1 raw material liquid    -   11 reaction container    -   23 fluorine gas pipe    -   23 a outlet    -   27 reaction inducer pipe    -   27 a outlet

1. A method for producing tetrafluoromethane, the method comprising: introducing fluorine gas to a raw material liquid containing a fluorinated hydrocarbon represented by chemical formula C_(p)H_(q)Cl_(r)F_(s) (in the chemical formula, p is an integer of 3 or more and 18 or less, q is an integer of 0 or more and 3 or less, r is an integer of 0 or more and 9 or less, and s is an integer of 5 or more and 30 or less) and having no carbon-carbon unsaturated bond and concurrently introducing a reaction inducer in a gas state, wherein the reaction inducer is reacted with the fluorine gas to induce a reaction of forming tetrafluoromethane from the fluorinated hydrocarbon and the fluorine gas and is at least one reaction inducer selected from a hydrocarbon gaseous at normal temperature and pressure and hydrogen gas.
 2. The method for producing tetrafluoromethane according to claim 1, wherein the reaction inducer is hydrogen gas.
 3. The method for producing tetrafluoromethane according to claim 1, wherein the fluorinated hydrocarbon is at least one fluorine-containing substance selected from a perfluorocarbon, a fluorohydrocarbon, a chlorofluorocarbon, a chlorofluorohydrocarbon, a chlorotrifluoroethylene polymer, and a perfluoropolyether.
 4. The method for producing tetrafluoromethane according to claim 2, wherein the fluorinated hydrocarbon is at least one fluorine-containing substance selected from a perfluorocarbon, a fluorohydrocarbon, a chlorofluorocarbon, a chlorofluorohydrocarbon, a chlorotrifluoroethylene polymer, and a perfluoropolyether. 